This article discusses the importance of Yiddish for our understanding of European Jewish histories and highlights some of the particularities of using Yiddish materials in historical research and the problems involved in doing so. There is a wealth of Yiddish materials available for historians yet many sources still need to be catalogued and disclosed. At the same time it is often not easy for historians to acquire the necessary linguistic skills to use Yiddish sources in their research, both because of practical reasons and a lack of awareness of the specific linguistic needs of historians. Opening up the field of Yiddish to historians though is very important to understand the rich and varied histories of Europe's Jews better, particularly before the Holocaust.